In hospitals, as well as emergency medical situations, it is a common practice when a patient is having difficulty breathing or not breathing at all to apply resuscitation to assist breathing. One approach is to use an endotracheal tube inserted in the patient's trachea to facilitate the passage of air into and out of the lungs to maintain proper respiration. Another approach is to use a bag-mask-valve system. Trained hospital clinicians and emergency medical specialists are concerned that the endotracheal tube is properly placed into the trachea and not into the esophagus. In the bag-mask-valve system, the medical professional's concern is proper cardio-pulmonary function. The patient's breathing must then be monitored over a relatively long period of time in order to ensure continuous respiration. Increasing concern for the proper placement of the endotracheal tube has alerted medical practitioners to seek every aid possible to ascertain the correct location of the endotracheal tube for short term and long term detection and monitoring.
Quantitative electronic analyzers provide an accurate reading of carbon dioxide levels but they are expensive, requiring minutes of warm-up time, frequent calibration and are not suitable for field use.
Fiberoptic laryngoscopes are also a method for determining accurate placement of the endotracheal tube but are very expensive, requiring specialized training. This method allows for determining correct placement but is of no value for long term patient monitoring.
Devices for the detection of carbon dioxide which use chemical compounds that change color when exposed to carbon dioxide are known in the art for determining and detecting the correct placement of an endotracheal tube into the trachea.
U.S. Pat. No. 4,691,701 discloses a method for detecting the correct placement of an endotracheal tube following intubation of a patient. The indicator is in the form of a transparent disc which sealingly engages an aperture in the housing. The disc has a chemical substance which produces a color change indication when exposed to carbon dioxide from a patient. Although this patent provides for a chemical substance applied to a litmus type paper, it requires a disk for connecting to the device and allows for a one time color change which occurs only for a very brief period.
U.S. Pat. No. 4,728,499 discloses a device for detecting carbon dioxide in a gas which comprises a housing having an inlet and an outlet with a clear visualization window for viewing the change of color of the chemically treated strip.
U.S. Pat. No. 4,994,117 discloses a device for detecting carbon dioxide in a gas which comprises a housing having an inlet and an outlet with a clear visualization window for viewing a chemically treated strip that provides various colors indicating the carbon dioxide concentration.
U.S. Pat. No. 5,166,075 discloses a method for determining the presence of carbon dioxide in a sample of respiratory gas in concentration of at least 2% within a diagnostically effective period of time (two to ten seconds) while an indication of the presence of carbon dioxide in a sample of ambient air (0.03% carbon dioxide) would be delayed beyond a predetermined period of time (ten minutes).
The various devices and compositions disclosed in the above mentioned patents provide means for detecting or indicating the presence of carbon dioxide under certain circumstances. However, none of the devices address the problem of a false positive indication of carbon dioxide. During intubation, residual levels of 0.5% to 1.5% of carbon dioxide may be in the airway and the esophagus and stomach which may indicate a color change to the practitioner and give the false sign that the tube is correctly placed in the trachea.
Also, none of the aforementioned patents discuss or address the problem of the ambient air sensitivity such indicators have when exposed to ambient air prior to use. Very careful attention must be placed to opening or exposing the device to ambient air immediately prior to use. This is very difficult due to the unpredictability of the timing of the procedure as to when to expose the device to ambient air prior to use, plus the fact that the practitioner is extremely preoccupied with the patient and would find any distraction not allowing as much pre-setup as possible as a severe disadvantage of the device.
Also the various prior devices address only determining the correct placement of an endotracheal tube and do not directly discuss the problems associated with monitoring the patient for a long period of time, either continuously or intermittently. It is known that the concentration of carbon dioxide in the atmosphere is about 0.03% and the concentration of carbon dioxide in the exhaled breath of a person is normally 4.0% to 5.0%.
However, none of the devices used to determine proper placement of an endotracheal tube in a trachea addresses the problem of false positive indication of carbon dioxide. Such false positive indication can occur when the endotracheal tube for example, is erroneously placed in the esophagus and the stomach contains residual levels of carbon dioxide high enough to cause a change in color on the carbon dioxide indicator. This will erroneously indicate that the endotracheal tube has been placed in the trachea.
One other problem with the foregoing devices is that they show a gradual color change which is proportional to the amount of carbon dioxide in the sample of gas being tested. Such gradual change of color makes it difficult to determine when the level of respiration of a person is sufficient. Additionally, none of the devices that are available exhibit insensitivity to exposure to ambient air before use. Such exposure to ambient air could cause a color change which may falsely indicate correct placement of an endotracheal tube in the trachea and proper respiration.
Another problem with prior devices is that they do not provide for low dead space. For instance, the maximum allowable dead space for a resuscitator per ASTM is 30 ml for adults, 15 ml for children and 7 ml for infants. One of the problems with known devices is that they add unacceptable levels of dead space. One of the known devices adds over 30 ml of dead space.